Environmental problem has been one of major issues, and thus, regulations for vehicle exhaust gas have been reinforced.
The auto industries focus on an exhaust system to reduce harmful element in exhaust gas, to reduce unburned gas, and to improve fuel consumption.
A conventional internal combustion engine includes two intake valves and two exhaust valves from which the exhaust gas is exhausted and joined at one exhaust port. In the conventional engine, reducing unburned gas within the exhaust gas is limited.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.